What Are Intestinal Parasites?

Intestinal parasites are either one-cell organisms or intestinal worms that live in the human intestines (small or large) and use the stool or blood from intestinal wall as a source of the food.

1. One-Cell Parasites – Protozoa

One cell organisms like Giardia lamblia, also called Giardia duodenale (Picture 1), cryptosporidium (crypto) and cyclospora utilize nutrients from the stool are part of Protozoa (Greek protos = first, zoa = animals). They may cause inflammation of the small intestine thus reducing its absorption capacity. Entamoeba hystolytica predominantly lives in the colon.

giardia

Picture 1. Parasite giardia from a stool sample,
as seen under the electron microscope (actual size:~0.01 mm)
(source: phil.cdc.gov)

2. Intestinal Worms (Helminths)

Intestinal worms (helminths) are common cause of diarrhea, bloating and malnutrition. They may cause severe infection (infestation), predominantly in children in areas with hot climates, bad hygiene and poor sewage disposal: in rural parts of Africa, Middle East, South Asia, Indonesia, and Central and South America. In Europe and North America, infestations are more sporadic.

Sources of Worm Infection

Eggs, shed in the stool of human or animals infected with adult worms, contaminate soil or water. Once outside the body, eggs need several days or weeks to develop into the infective stage – cysts or immature worms (larvae) that may be ingested when eating with soil-contaminated hands or with raw unwashed vegetables. Larvae may also penetrate a person’s skin during swimming or walking barefoot. When they reach the small or large intestine they grow into adult worms. Another source of intestinal worms is undercooked infected meat of domestic pig, freshwater fish or wild animals (bear, walrus etc). One can also be infected from ingesting dog’s fleas that have ingested parasitic eggs. Children may contract infection from sandboxes contaminated with pet’s stool.

Pathology of Intestinal Worms

Adult worms (from 1 millimeter to several meters long) invade the bowel wall and suck the blood from it or live freely in the intestine and utilize nutrients from the bowel content. The result are small intestinal or colonic inflammation and ulcers, anemia, protein, iron and vitamin (mainly A, C, B12) deficiency. Intestinal obstruction may occur in severe cases. Larvae may migrate to other organs (liver, spleen, bladder, muscles, lungs, brain) where they form cysts and trigger allergic inflammation.

Roundworm

Picture 2. Roundworm

Worms Commonly Causing Diarrhea in Human:

A. Roundworms:

  • The large roundworm (Ascaris lumbricoides) are about 30 cm long and found worldwide
  • Hookworms (Necator americanus, Ancylostoma duodenale) are about 1 cm long; they suck blood from the intestinal wall
  • Whipworm (Trichuris trichiura)
  • Threadworms (Strongyloides stercoralis)
  • Trichinella spiralis

B. Flukes:

  • Schistosoma mansoni. Symptoms after invasion into other organs may include enlarged liver and spleen, jaundice, abdominal swelling (ascites), urinary bleeding, coughing blood, muscular aches and seizures.

C. Tapeworms:

  • Fish (broad) tapeworm (Diphyllobothrium latum) is contracted by infected freshwater fish, may exceed 10 m, it appears in Europe, Russia and US
  • Beef tapeworm (Taenia saginata) and pork tapeworm (Taenia solium) are contracted by undercooked beef or pork in rural areas, worldwide; adult worms may be over 20 m long

How Can be Parasites Contracted?

Parasites are shed in human or animal stool; the source of infection in poor countries is usually stool-contaminated food or drinking water, and in industrialized countries, recreational water (lakes, pools) or homosexual men.

Symptoms of Intestinal Parasites

Intestinal parasites may cause one or more of the following symptoms:

  • Mild diarrhea, appearing few days to several weeks after the travel or ingestion of contaminated food, having waxing and waning course and lasting for several days to months is a characteristic symptom of parasitic diarrhea (in comparison with bacterial diarrhea with sudden and dramatic onset within some hours after food ingestion).
  • Parts of worms may be sometimes found in the stool. Swollen itchy spot on the skin (usually foot) denotes parasite entry. Itchy anus, swelling around the eyes, and skin rash are also common. Intestinal worms may find their way out through the mouth or nostrils during the sleep.
  • Mucus in the bowel movement
  • Bloating and flatulence
  • Intestinal worms or their parts may be found in the stool.
  • Weight loss is common.
  • Pale skin, tiredness, tingling (due to reduced absorption of minerals and vitamins).
  • Entamoeba histolytica may cause severe colitis with ulcers, abdominal cramps, blood in the stool with occaional pus – the disease is known as amebic dysentery (9). Entamoeba may invade liver, lung, brain, or other organs, where it forms cysts.
  • Infection by one-cell organisms or intestinal worms is often present without any symptoms.

Diagnosis of Intestinal Parasites

Diagnosis can be made on the basis of:

  • Symptoms (see above)
  • History of a recent travel from area with high to area with low hygiene standards
  • Ova and parasites (O&P) test of the stool is often false negative so three stools from three different days (at least two days apart) should be tested.
  • Hemoccult test may reveal blood in the stool (often in Entameba hystolytica or intestinal worms)
  • Blood testsoften reveal elevated eosinophils and IgE antibodies (also elevated in allergies and other conditions); low ferritin, hemoglobin or red cells may be due to worms that suck blood from the intestinal wall
  • CT or biopsy are needed to determine involvement of other organs like liver and lungs

Treatment of Intestinal Parasites

  • For giardia and cryptosporidium antibiotic metronidazole 3 times a day for at least 3 days should be taken. Other effective drugs include: quinacrine, tinidazole (a single dose), furazolidone, and paramomycin  that is not absorbed so it may be used in pregnancy (1).
  • For cyclospora trimethoprim-sulfametoxazolis used. In giardia, tinidazole is also effective.
  • Entamoeba hystolytica is treated with metronidazole or tinidazole (1).

Treatment of Intestinal Worms

A single dose of anti-worm drugs: mebendazole (safe for pregnant women), albendazole, diethylcarbamazine, ivermectin or praziquanteltreat parasites in most cases. For some days after the healing, a stool-to-mouth autoinfection with eggs is still possible. Untreated infestations may last for years.

Intestinal parasites are usually successfully treated but may reoccur if the source of infection still exists.

Prevention of Infection

Infection by intestinal parasites can be prevented by:

  1. Hand washing with soap before eating and after bowel movement
  2. Food cooking kills all parasites (but smoking or freezing does not)
  3. Washing of raw vegetables and fruits
  4. Travelers from western countries visiting Central or South America, Africa or South Asia should ingest only packaged, bottled or cooked foods and drinks and only fruits that they can peel by themselves. Read about food disinfection in the article about travelers diarrhea.

For How Long is a Person with Parasitic Diarrhea Contagious?

Stool of a person with intestinal parasites is contagious as long as infection lasts. The stool of a person, infected by Entamoeba hystolitica may remain contagious for years after diarrhea is healed.

Related Articles:

References:

  1. Intestinal protozoa (tulane.edu)
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Further Reading :
  • Stool Analysis and Blood Work Results in Gastrointestinal Disorders
  • Chronic Stomach and Bowel Infections – Symptoms & Treatment